The UN's International Maritime Organization IMO introduced requirement for on-load release hooks on all ships applicable for all ships built after Jul. 1, 1986 to ensure that the lifeboats could be released easily and quickly in an emergency evacuation situation.
There are three types of lifeboat releasing mechanism, on-load and off-load release and release hooks for free fall lifeboats. The first two mentioned mechanisms release the lifeboat from the lowering mechanism or davit, which is attached to a wire or loop. By releasing the loop, the lifeboat can be set free to propel away from the ship.
Lifeboats with off-load mechanism may only be released when the lifeboat is into the sea and fully buoyant and hence the fall is un-loaded. Release require manual action by the lifeboat crew—a dangerous action often proved difficult as even un-loaded falls may be influenced by outside forces from the mothership's possible remaining speed through the water, wind, waves, heeling etc.
An on-load mechanism can release the lifeboat from the wire, with the lifeboat above the water level and with all the crewmembers onboard the boat. The load will be still on the fall as the lifeboat would not have touched the water. A release handle or similar is provided onboard inside the lifeboat to operate this mechanism.
The third release mechanism is hook for free-fall lifeboats. In these types of lifeboats there is only one hook, arranged at the rear end of the lifeboat, holding the lifeboat. When this hook is released, the lifeboat drops into the water.
Traditionally, lifeboats were suspended from two off-load hooks. It is therefore impossible to release loaded hooks, and it could also be problematic to release the hooks with certainty and simultaneously, even with the lifeboat in the water, especially during evacuation in high seas.
There are many weaknesses also with the existing on-load release systems. There have been cases where the lifeboats have dropped during exercises, both during lowering and hoisting, with or without people onboard. These accidents often occur from the deck of the ship when the lowering or lifting process gets to a stop or a significant jerk occurs.
There could also be a failure because the on-load hooks are not properly reset. These hooks can release unintentionally when hoisting the lifeboat or during the next lowering of the lifeboat.
There is also a problem that one of the hooks may release unintentionally alone or before the other one releases. This has on occasions led to a situation where the lifeboat has fallen upside down into the water.
Other reasons for failure are lack of maintenance of the hooks or an overly complex construction of the on-load hooks, so that there is a risk that the parts of the hooks are not assembled correctly.
Lack of skills of the person who is to release or secure of the on-load hooks is also a cause for accidents.
Other reasons for failure of on-load hooks are the use of wrong materials in the hooks.
Due to the many dramatic accidents, some of them fatal, with the new on-load release mechanisms, the IMO has changed the regulations, so that it is no longer a requirement to have people aboard lifeboats during the lowering and reversible handling during exercises. This has led to fewer accidents, but has increased the seafarers' skepticism to the lifeboat as a lifesaver. Is it considered dangerous to be in the lifeboat during exercise, leading to the view that it is even more dangerous to be in the lifeboats during emergency situations.
Publication US20120125252 shows a coupling for coupling a fall to a lifeboat. The coupling comprising a locking portion that has the shape of a spherical ball and a receiving portion shaped as a hollow. In the locked position, the locking portion is secured within the receiving portion by a spring or a pawl when the fall is slack. To release the locking portion from the receiving portion, actuators are pushing the locking portion from the receiving portion. When the fall is slack it is just the spring or pawl that is preventing the release of the locking portion. If there is a failure in the spring or pawl, this could lead to unintentional release. There is also no easy retrieval of the coupling without the use of hands.
Publication U.S. Pat. No. 4,610,474 shows a release hook for lifeboats. It comprises a hook with spaced apart guide pins. Supporting plates with spaced apart guide slots are affixed to the lifeboat. The guide pins of the hook are engaging in the guiding slots of the supporting plates, and the hook is adapted to move between a loop-engaging loaded position and a loop disengaging position. The hook is also the release mechanism and is moved within the guide slots by a piston pushing against the lower part of the hook. A bolt pin or stop secures the cable or chain link attached to the lowering arrangement inside the hook. In this publication, the cable or chain link is attached to the movable hook and the hook is also receiving the total load acting on the hook arrangement.
This results in an undesirable and dangerous strain on the hook as the moveable hook has to carry the full load of the lifeboat, a failure in the hook could result in an accidental release of the hook and lifeboat from the lowering arrangement.
GB292259 and GB225591912 both shows another lifeboat hook assemblies comprising a hook-shaped beak and a release mechanism, the release mechanism is adapted to move relative to the hook shaped beak between a locked position and a released position.
In publication GB292259, the hook shaped beak having a guide pin slidably connected to a guide slot in the release mechanism.
None of the publications shows a lifeboat hook assembly where the release mechanism having at least two guide pins adapted to engage with corresponding guide slot in the hook shaped beak. This provides a more reliable and secure hook assembly than the previous publications.